The present invention relates to a power transmission for a mechanical press for transmitting driving force of a main motor to a slide drive, a work conveyance drive or the like.
In some conventional mechanical press, a die-supporting slide is driven by a slide drive to press a work. In time with the pressing operation, a work conveyance drive is driven to convey a work. Thus, works are continuously formed into products.
FIG. 1 shows an example of a power transmission for transmitting driving force to such slide and work conveyance drives. A main motor 1 is driven to rotate a flywheel 2 and store rotational energy in the flywheel 2. A clutch 3 is then clutched or engaged to the flywheel 2 to transmit the rotational energy stored in the flywheel 2, as driving force, to a power transmission shaft 4. The driving force is taken by a power take-off gear 5 on the shaft 4 and is transmitted through a junction gear 6 to a pinion 7 coaxial with the gear 6. The pinion 7 is rotated to drive a slide drive 8 so that a slide 9 which supports a die is driven to carry out a pressing operation. At the same time, the rotation of the junction gear 6 is also transmitted through a bevel gearing 10 or the like to a work conveyance drive 12. Reference numeral 11 denotes a brake for the power transmission shaft 4.
In the above-mentioned conventional power transmission, for structural reasons, movements of the drives 8 and 12 can be controlled only by selective engagement and disengagement of the clutch 3 and volocity-control of the flywheel 2. Therefore, for example, action velocity of the slide 9 cannot be controlled during a stroke of movement of the slide 9; pressing working cannot be carried out with the slide 9 being temporally stopped at its bottom dead point of movement. As a result, pressing working for different kinds of materials is considerably limited.
In the conventional power transmission, the slide drive 8 is actuated by engaging the clutch 3 to the flywheel 2 which is rotating; this causes mechanical shock and big noise. Moreover, structurally the clutch 3 requires connection pads such as friction inserts, which are consumables; this requires a great number of pads being prepared for exchange and periodic maintenance has to be carry out for checking whether the pads being used are to be exchanged or not.
In view of the above, a primary object of the present invention is to provide a power transmission for a mechanical press which can control action velocity of a slide or the like to non-limitatively carry out press working for different kinds of materials and which employs no clutch, which is a cause of mechanical shock and requires consumables to be exchanged, to thereby carry out press working with no maintenance for consumables and with lower cost.
To attain the above object, in a power transmission wherein rotational energy stored in a flywheel is taken through a power transmission shaft by a power take-off gear and is transmitted to a drive, the present invention resides in that the power transmission shaft is divided into first and second shaft sections adjacent to the flywheel and the power take-off gear, respectively, a planetary gearing being arranged between the shaft sections and adapted to be driven by a servo motor, the power take-off gear being mounted on an output section of said planetary gearing.
In another aspect of the invention, a planetary gearing is arranged between the shaft sections and has at its portion a variable torque brake which is controlled by a control unit.
In a further aspect of the invention, a planetary gearing is arranged between the shaft sections and is driven by a servo motor. The power take-off gear and a brake is arranged at an output section of the planetary gearing. An on-off coupling which may be a gear coupling is arranged between the flywheel and the first shaft section.
A differential gear may be arranged to return part of output from the planetary gearing to an input section thereof and may be connected to a servo motor.
The slide drive may be provided with a load cell which detects any overload acting of the slide to transmit a signal from the load cell to the servo motor.
When the planetary gearing is arranged between the shaft sections as mentioned above, the rotational energy of the flywheel is transmitted through the first shaft section to the planetary gearing and is taken by the power take-off gear. By controlling rotation of a part of the planetary gearing, rotational velocity of the power take-off gear can be varied so that action velocity of the drive can be freely or arbitrarily controlled. Thus, the action velocity of the slide or the like can be controlled during a stroke of movement thereof.
When the variable torque brake is arranged, in place of servo motor, at a part of the planetary gearing, the rotational velocity of a part of the planetary gearing can be controlled by the torque brake, which varies the rotational velocity of the power take-off gear so that action velocity of the drive can be freely controlled.
When the power take-off gear and the brake are provided at the output section of the planetary gearing driven by the servo motor and the rotational velocity of the servo motor is set to a calculated value with the drive being braked to stop, the rotational velocity of the first shaft section of the power transmission shaft can be made equal to that of the flywheel. This makes it possible to employ a connector such as gear coupling between flywheel and the power transmission shaft which requires no consumables such as connection pads. To vary the rotational velocity of the power take-off gear can be attained by controlling the rotation of the output section of the planetary gearing by means of the servo motor so that action velocity of the drive can be freely controlled.
When the differential gear is provided to return part of output of the planetary gearing to an input section thereof and is connected to the servo motor, braking force required for the servo motor can be minimized.
When any overload is detected by the load cell, the servo motor may be tripped or driven at a predetermined rotational velocity to nullify overload.